docs: def add_subplot(self, x, y, n, margin=0.05):
          """Creates a div child subplot in a matplotlib.figure.add_subplot style.
  
          Parameters
          ----------
          x : int
              The number of rows in the grid.
          y : int
              The number of columns in the grid.
          n : int
              The cell number in the grid, counted from 1 to x*y.
  
          Example:
          >>> fig.add_subplot(3,2,5)
          # Create a div in the 5th cell of a 3rows x 2columns
          grid(bottom-left corner).
          """
          width = 1./y
          height = 1./x
          left = ((n-1) % y)*width
          top = ((n-1)//y)*height
  
          left = left+width*margin
          top = top+height*margin
          width = width*(1-2.*margin)
          height = height*(1-2.*margin)
  
          div = Div(position='absolute',
                    width='{}%'.format(100.*width),
                    height='{}%'.format(100.*height),
                    left='{}%'.format(100.*left),
                    top='{}%'.format(100.*top),
                    )
          self.add_child(div)
          return div